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The compositional dependence of the thermal conductivity of a molten copper-iron (Cu-Fe) alloy at low Fe contents was measured herein by combining a periodic laser heating method and an electromagnetic levitator (EML) with a static magnetic field that can suppress the melt convection in the molten sample. The measured thermal conductivities markedly decreased with the composition of Fe up to 20 at. pct. [ABSTRACT FROM AUTHOR]

The thermal conductivity of molten copper was measured by the periodic laser-heating method, in which a static magnetic field was superimposed to suppress convection in an electromagnetically levitated droplet, to extend the measurement range of the method up to a relatively high thermal conductivity. Before measuring the thermal conductivity, the optimum conditions for static magnetic field, the laser frequency of periodic heating and sample diameter were investigated by numerical simulation both for the flow and thermal fields in an electromagnetically levitated droplet and for the periodic laser heating of the droplet in the presence of melt convection. As a result, the temperature dependence of the thermal conductivity of molten copper was proposed in the temperature range between 1383 and 1665 K. In addition, by comparing our results with those of previous studies, it was demonstrated that the present method of measuring thermal conductivity is also available for molten materials with a relatively high thermal conductivity, such as molten copper. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate quantitatively the effect of melt convection in an electromagnetically levitated molten droplet on the thermal conductivity of liquid silicon measured by the electromagnetic levitation (EML) technique superimposed with a static magnetic field, the numerical simulations for melt convection in the droplet and additionally, for the measurement of thermal conductivity were carried out. In addition, the thermal conductivity of molten silicon was measured by the EML technique, and then compared with those obtained numerically. In the numerical simulations of melt convection, the buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered as the driving forces of convection. As a result, the numerical simulations could sufficiently explain the measurement of thermal conductivity by the EML technique under a static magnetic field. Also, it was suggested that a magnetic field of more than 4T should be applied to measure the real thermal conductivity of molten silicon by the EML technique. [Copyright &y& Elsevier]

Abstract: Recently, a novel method of measuring the thermophysical properties, particularly thermal conductivity, of high-temperature molten materials using the electromagnetic levitation technique has been developed by Kobatake et al. [H. Kobatake, H. Fukuyama, I. Minato, T. Tsukada, S. Awaji, Noncontact measurement of thermal conductivity of liquid silicon in a static magnetic field, Appl. Phys. Lett. 90 (2007) 094102]; this method is based on a periodic laser-heating method, and entails the superimposing of a static magnetic field to suppress convection in an electromagnetically levitated droplet. In this work, to confirm the fact that a static magnetic field really suppresses convection in a molten silicon droplet in an electromagnetic levitator, numerical simulations of convection in the droplet and periodic laser heating in the presence of convection have been carried out. Here, the convections driven by buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered. As a result, it was found that applying a static magnetic field of 4T can suppress convection in a molten silicon droplet enough to measure the real thermal conductivity of molten silicon. [Copyright &y& Elsevier]

Abstract: Recently, a novel method of measuring the thermophysical properties, especially thermal conductivity, of high-temperature molten materials using the electromagnetic levitation technique has been developed by [H. Fukuyama, H. Kobatake, I. Minato, K. Takahashi, T. Tsukada, S. Awaji, Establishment of noncontact AC calorimetry of high-temperature melts using solid platinum spheres as a reference, in: Proceedings of 16th Symposium on Thermophysical Properties, CD-ROM, 2006, p. 937; H. Kobatake, H. Fukuyama, I. Minato, T. Tsukada, S. Awaji, Noncontact AC calorimetry of liquid silicon with suppressing convections in a static magnetic field, in: Proceedings of 16th Symposium on Thermophysical Properties, CD-ROM, 2006, p. 625], where the method was based on periodic laser-heating, and a static magnetic field was superimposed to suppress convection in an electromagnetically levitated droplet. In the present work, the periodic laser-heating method was modeled to estimate the thermal conductivity and emissivity of the electromagnetically levitated droplet using a measured parameter, i.e., the phase lag between the modulated light and the temperature variations detected by a pyrometer, Δϕ s, at various frequencies of the modulated light ω. Here, the unsteady-state heat conduction equation for the droplet accompanying radiative heat transfer to the ambient was simplified and transformed to steady-state linear equations. The experimental relation between Δϕ s and ω was fitted by the mathematical model proposed here to estimate simultaneously the thermal conductivity and emissivity of molten silicon. Also, the numerical simulations for unsteady thermal field in the electromagnetically levitated droplet which was periodically laser-heated were carried out to demonstrate the validity of the proposed simplified model, and then to investigate the sensitivity of the thermophysical properties to the relation between Δϕ s and ω. [Copyright &y& Elsevier]

Thermal conductivity of liquid silicon is indispensable for numerical modeling of silicon crystal growth processes and for elucidating electron transport phenomena in high-temperature liquids. However, crucial obstacles render measurement of thermal conductivity difficult: convection and contamination from contact materials. In this study, the authors developed a noncontact measurement of thermal conductivity of liquid silicon using electromagnetic levitation in a static magnetic field. Convection in the levitated silicon becomes negligible above 2 T. The determined thermal conductivity shows that the electron contribution is dominant for thermal transport in liquid silicon at temperatures of 1750–2050 K. [ABSTRACT FROM AUTHOR]

Highlights • Three-dimensional simulations of electromagnetically levitated molten droplet were conducted. • Comparisons of the convection under vertical, horizontal and rotational magnetic fields are performed. • The rotational magnetic field shows potential advantages in thermal conductivity measurement, stirring and solidification of melts. Abstract A series of three-dimensional numerical simulations was conducted to investigate the convection inside an electromagnetically levitated silicon droplet under vertical, horizontal and rotational magnetic fields, respectively. The results show that the flow is totally axisymmetric and two counter-circulating vortexes appear in the droplet with an inner-outer distribution under vertical magnetic fields. The inner vortex brings fluids from the top area to bottom area directly, which is potentially responsible for the requirement of quite strong vertical magnetic fields in the experimental measurement of thermal conductivity of molten silicon. With horizontal magnetic fields, the vortexes inside the droplet turn to an up-down distribution, which is more beneficial in the thermal conductivity measurement since it prevents the direct convective heat transfer effectively. However, the horizontal magnetic field fails to suppress the convection effectively and the flow is intense and spatially imbalanced, leading to a less stable flow state. The rotational magnetic field combines the advantages of the formers, suppresses the convection along z-axis apparently and creates an up-down distribution of vortexes simultaneously. It suggests that the rotational magnetic field shows potential interest in the measurement of thermal conductivity of melts. Besides, the rotational magnetic field would evoke forced convection in azimuthal direction, which can be better controlled by varying magnetic intensity and rotating frequency. The azimuthal flow is expected to balance the rotation of melts induced by helicity of coils in experiments and shows potential advantages in melt stirring and solidification from undercooled melts. [ABSTRACT FROM AUTHOR]

Abstract: Densities and thermal conductivities are reported for a series of N-alkylpyridinium tetrafluoroborate compounds with butyl (N-butylpyridinium tetrafluoroborate), hexyl (N-hexylpyridinium tetrafluoroborate) and octyl (N-octylpyridinium tetrafluoroborate) groups. The densities were measured with a vibrating tube densimeter over the temperature range 293–353K at pressures ≤20.0MPa. The transient short hot wire method was used to measure thermal conductivity over the temperature range 294–335K at pressures ≤20MPa. It was found that the effect of alkyl chain length on thermal conductivities in N-alkylpyridinium tetrafluoroborates is the same degree as 1-alkyl-3-methylimidazolium tetrafluoroborates. The experimental values at 293K and 0.1MPa were consistent with the predicted values proposed by Fröba et al. [Copyright &y& Elsevier]